Conventionally, in this kind of floating type brake disc, there are formed: pin-receiving portions at a circumferentially plurality of positions on an inner circumference of a rotor, each of the pin-receiving portions being projected radially inward and having a semi-circular notch at a radially inner end; and pin-receiving portions at a circumferentially plurality of positions on an outer circumference of a hub, each of the pin-receiving portions being projected radially outward and having a semi-circular notch at a radially outer end. By butting together the pin-receiving portions of the rotor and the pin-receiving portions of the hub, there are formed pin openings by the notches of both the pin-receiving portions so that a connecting pin can be inserted into each of the pin openings (see, e.g., patent document 1).
By the way, at the time of braking, the rotor is heated to a high temperature due to sliding contact of the rotor with a brake pad. The heat will then escape to the hub side through the pin-receiving portions of the rotor and through the connecting pins. In the above-described conventional example, since there is formed, at the radial end of each of the pin-receiving portions of the rotor, the notch to receive therein half the circumference of the connecting pin, the amount of escape of heat through the pin-receiving portion becomes large. As a result, the rotor gives rise to an unevenness in temperature with a large temperature difference. Should this phenomenon be repeated at each time of braking, there is a possibility of giving rise to thermal distortion of the rotor.
As shown in FIG. 5, there is also known an example in which a pin-receiving portion b of a rotor “a” is formed so as to enclose a connecting pin c from diametrically outside of and circumferentially one side of a brake disc. Also there is formed a pin-receiving portion e of a hub d so as to enclose the connecting pin c from a diametrically inner side of and the circumferentially opposite side of the brake disc (see, e.g., patent document 2).
In this example, the area of contact of the pin-receiving portion b of the rotor “a” with the connecting pin c becomes smaller than the one as described in patent document 1. As a result, the escape of heat through the pin-receiving portion b can be limited to a certain degree. However, the pin-receiving portion b of the rotor “a” has a portion b1 that encloses the connecting pin b from the diametrically outside of the brake disc. Therefore, the escape of heat occurs from this portion b1, and the escape (transmission) of heat cannot be sufficiently limited.
In addition, the hub is generally made of an aluminum alloy, and the rotor is formed of stainless steel in order to secure heat resistance. In order to reduce the weight of the brake disc, it is necessary to reduce the weight of the rotor that is formed of stainless steel having a high specific gravity. For that purpose, it becomes necessary to minimize the size of the pin-receiving portion of the rotor to the extent possible. In the example as shown in patent document 2, the pin-receiving portion b of the rotor “a” becomes smaller than the one as shown in patent document 1. However, in order to attain a further reduction in weight, it is desired to cut away the above-mentioned portion b1 from the pin-receiving portion b.
In the floating type brake disc, there is inserted onto an external surface of the connecting pin a disc spring (urging means) which connects the rotor and the hub in a floated state by urging the two members in the axial direction. Since the disc spring is subjected to repeated elastic deformation due to various kinds of loads to be operated when the disc brake is put into operation, the disc spring is required to have high durability. As a solution, patent document 3 discloses one in which the disc spring is made up of a disc-like flat plate portion which has formed therein an opening to enable the disc spring to be inserted onto an external surface of the connecting pin; and a skirt-like elastic supporting portion which is provided on an outer circumference of the flat plate portion.
However, in the example described in the patent document 3, the outer peripheral edge of the elastic supporting portion is substantially in linear contact with the axial surfaces of the rotor and the hub in a connected state. Therefore, whenever it is subjected to elastic deformation when load is applied (the elastic deformation being such that the elastic supporting portion is deformed under load in a manner to expand, or is restored back to the original state as a result of removal of the load), the outer peripheral edge of the elastic supporting portion slides in frictional contact with the axial surfaces of the rotor and the hub. As a result, there is a problem in that the surfaces of the rotor and the hub wear out. In this kind of case, if the rotor and the hub have applied to the surfaces thereof a plating of Ni and the like for the purpose of rust prevention and the like, there is a possibility that the plating layer is damaged or peeled off. In this case, it is considered to interpose, e.g., a washer between the axial surfaces of the rotor and the hub and the disc spring. This solution, however, brings about an increase in the number of constituting parts, resulting not only in an increase in cost but also in a troublesome work of connecting the rotor and the hub together.